Keitel, Christoph H. Division Prof. Dr. Christoph H. Keitel, MPI for Nuclear Physics, Max Planck Society;
http://link.aps.org/doi/10.1103/PhysRevA.51.2575 (Publisher version)
Buzek, V., Keitel, C. H., & Knight, P. L. (1995). Sampling entropies and operational phase-space measurement. I. General formalism. Physical Review. A, 51(3), 2575-2593. doi:10.1103/PhysRevA.51.2575.